The early chess magazines have been locked away in specialist libraries for many years. Assuming that they have not been picked over completely, what more information about the early unofficial events can be gleaned from their pages?
I started chronologically, tackling the earliest matches first, noting the location of different early articles about the matches. This page in particular caught my attention.
The Chess Player's Chronicle [S01V03; 1842], p.410
The page is titled,
SUMMARY OF THE GAMES
PLAYED BETWEEN M. DE LA BOURDONNAIS AND MR. M'DONNELL
The lead paragraph says,
In concluding the series of games between these distinguished Champions, it may not be uninteresting to review briefly the results of their several contests. It appears that in all, they played together EIGHTY-FIVE GAMES, divided into four separate matches of twenty-one games each, and one extra game.
This is contrary to conventional wisdom, which says the games were played in a series of six matches of varying length, between 9 and 25 games per match. That's what I've recorded on my own page, World Chess Championship : 1834 Labourdonnais - McDonnell Matches, which I double-checked against Gelo's book 'Chess World Championships 1834-1984'; see Acknowledging an Important Source (January 2019) for more about the book.
The summary in 'Chess Player’s Chronicle' (CPC) gives the following scores for the four matches. The +/- tallies are from the Labourdonnais point of view:-
This maps fairly well onto the sequential score given by the conventional view of six matches. For example, the score of the first 21 games of the first match was +13-4=4, which is the same as the CPC tally. There are, however, a few differences arising in subsequent matches. These might be accounted for by the choice of the 85th game, CPC's 'one extra game'. While I have no reason to doubt the accuracy of the conventional view, I'll keep the discrepancy in mind while I review other material on the match.
Later: Re 'I have no reason to doubt the accuracy of the conventional view', that view is from an essay by George Walker. I discussed his book 'Chess and Chess-players: Consisting of Original Stories and Sketches' last year in Chess-books and Chess-players (July 2018), including a link to access a copy. The last chapter is titled 'The Battles of M'Donnell and De La Bourdonnais' and starts with a poem by Percy Bysshe Shelley.
"The splendors of the firmament of time
May be eclipsed—but are extinguished not.
Like stars, to their appointed height they climb,
And death is a low mist, which cannot blot
The brightness it may veil."
The literary tone continues with the first paragraph.
ALL the world -- at least all the world we care about upon the present occasion, the Chess world -- has heard of the Chess encounters of De la Bourdonnais and M'Donnell. The battle has been sung by Mery in French, by D'Arblay in English. The games themselves have been printed in several different European languages, and have become a code of precedents, like the famed Pandects of Justinian, by the light of which future players may walk safely through almost all the dark mazes of the Sacred Grove -- if they have but the intellect to understand, and the memory to apply these splendid examples of Chess-play to the varied situations which arise during the progress of an actual game.
A note to the essay mentions, 'This paper was first published in the Chess Player's Chronicle, 1843.' It was the last article in CPC volume 4, signed by George Walker and dated October 1843. I'll use the CPC version for the rest of the quotes in this section. Later in the essay G.Walker writes,
Mr. William Greenwood Walker, himself but a very moderate Chess-player, (related to me only in name,) was the most enthusiastic Chess-recorder I have ever had the honour to know. He cared little to play himself, but delighted to be always at M`Donnell's elbow, to record his victory ; like one of the bards of old, ever by the side of his Chief to hymn the song of triumph in his praise. Mr. Walker took down the whole of the games played by M'Donnell and La Bourdonnais, and printed them, with many others played by the former, in a well known octavo volume. Without him, these fine games would have been lost for ever. Great, then, is the obligation we are all under to his name, for thus constantly attending at his post—the scribe, the herald of the war. It is no light thing to sit daily five or six hours, during a period of months, to watch games playing, and write them down. Mr. William Greenwood Walker has been taken from us long since. He died full of years. We could "well have spared a better -- aye, many a better -- man."
As for the structure of the matches, he writes,
I intend to be the more particular in presenting what may be termed the statistics of the games played by M‘Donnell and De la Bourdonnais, as they have been on many occasions so erroneously stated. Writers of these latter times have assumed that they were all comprised within two, three, or four matches. Be it mine to state the exact and full truth. During the time they were playing, I visited the club daily, and took some of the games down, move by move, as they were played; relieving my worthy namesake thus occasionally at his post. At the close of each day's play, the notes of Mr. Greenwood Walker were kindly placed at the disposal of Mr. [William] Lewis and myself; who thus were enabled to get the games in a complete shape. I have them all by me, as I wrote them out at the time -- in the exact order they were played, and classed according to the actual matches of which each one formed a part.
Following that are page after page of 'the exact and full truth'. These correspond to the conventional wisdom and are undoubtedly the source of what we know about the first (unofficial) World Championship event.